The pericardium is the outermost layer of the heart, surrounding the myocardium. The pericardium consists of two layers: an outer fibrous layer, and an inner serous layer. The inner serous layer is further sub-divided into two layers: an outer parietal layer, and an inner visceral layer. The inner visceral layer is referred to as the epicardium, and immediately covers the myocardium and the great vessels of the heart. Situated between the parietal layer and the epicardium is the pericardial cavity, a fluid-filled space typically containing approximately 20-25 mL of physiological fluid.
Certain cardiac conditions are treated by percutaneously inserting a needle through the outer layers of the pericardium into the pericardial cavity, and performing a treatment procedure from within the pericardial cavity. For example, ventricular tachycardia is often treated by inserting a needle into the pericardial cavity to provide access to the epicardium for catheter mapping and ablation procedures (Valderrabano et al. (2004), Heart Rhythm 1(3):311-6; Sosa et al. (2000) J Am Coll Cardiol 35:1442-9). This technique uses a standard epidural needle, which is inserted into the subxiphoid region, to puncture both the thoracic cavity and the outer layers of the pericardium. Once the needle has reached the pericardial cavity, catheter mapping and ablation procedures are performed on the epicardium.
This technique, however, has various risks associated with it, the most notable of which is the laceration of the myocardium by the needle. This risk is heightened in cases where the pericardial cavity and fluid volume is small. One report found accidental right ventricular laceration occurred in greater than 7% of patients (Sosa et al. (2000) J Am Coll Cardiol 35:1442-9).
The prior art includes alternative methods of accessing the pericardial cavity, but the methods described are relatively invasive and carry further risks to the patient.